What to do if the screed is crumbling?
I have faced a very unpleasant problem. At one time when we poured the screed (about 100 meters) we decided to add glue for ceramic blocks into the mix. In appearance, the screed turned out good. The difference is minimal, there are no cracks (even micro).
But when we started to prepare for installation of the flooring (to glue plywood and put it on dowels), it turned out that the screed began to crumble. Plywood peeled off along with the top layer of screed, dowels go out very easily.
Frankly speaking, there is no desire to remake screed. Found this option solutions: A lot of primer + poured floor. With poured flooring, the hardwood floor is already laid in a floating manner.
I think you just have to give up plywood and hardwood flooring in favor of regular laminate.
Instead of primer, buy PVA glue, dilute it with water and pour it over. It will be cheaper and more durable.